1. Field of the Invention
The present invention generally relates to a lamp circuit providing a plurality of lamps connected in series, and more particularly, to a lamp circuit providing a means for identifying which lamp is disconnected.
2. Description of the Prior Art
For runway lighting in an airport, series lamp circuits are generally employed. The series lamp circuit includes current transformers, each of which provides a secondary winding connected with a corresponding lamp and a primary winding connected in series with each other, and a constant-current regulating circuit for supplying constant current through the secondary coils connected in series so that the constant current is supplied through each lamp, thereby allowing each lamp to be lighted at constant brightness.
The lamp circuit designed as above has already had a proposed invention about a disconnected lamp detecting device for detecting the occurrence of disconnection as well as the quantity of disconnected lamps (see U.S. Pat. Nos. 4,295,079 and 4,396,868). Those conventional disconnected lamp detecting devices, however, are incapable of identifying which lamp is disconnected. Hence, once the device detects the occurrence of disconnection, it is necessary for maintenance operators to check which lamp is disconnected by moving around a runway in an airport. This is quite inefficient.
Furthermore, if the replacement of the disconnected lamp is retarded, the secondary winding of the transformer connected to the disconnected lamp is left open for a long period of time. In this condition, there is a danger of a winding short upon the application of a light voltage and of a burn-out due to rising temperature.